Packing containers with openable bellow-type folded top closure, which may be either ridgelike upright or more or less flat, constitute an example of well-known consumer packages of non-returnable character for liquid contents such as milk and similar dairy products. The packages are manufactured customarily with the help of modern, high-capacity packing machines which form, fill and close the finished packages. It is required of these consumer packages that they should be inexpensive, easy to distribute and handle and, not least, easy to open, so that the contents can readily be made accessible when desired.
A large group of non-returnable packages, for e.g. milk, consist of a rigid carrier layer of paper or cardboard which at least on one side has a coating of a thermoplastic material which imparts to the package the required liquid-tightness and other desirable barrier characteristics, e.g. gas-tightness, and which at the same time makes possible tight and durable sealing joints, in that combined layers of plastic material are heated and at the same time pressed to one another, so that a fusing together of the surfaces of the combind plastic layers is obtained. Since most packages of this type during handling are at risk of coming into contact with moist media, it is customary, moreover, for the outsides of the packages too to be coated with a plastic layer preventing moisture from penetrating into the fibrous carrier layer which, on becoming moist, loses its mechanical rigidity and causes the package to feel soft and difficult to handle.